It has been discovered that the medical outcome for a patient suffering from severe brain trauma or from ischemia caused by stroke or heart attack is degraded if the patient's body temperature rises above normal (38.degree. C.). It is further believed that the medical outcome for many such patients might be significantly improved if the patients were to be cooled relatively quickly to around 32.degree. C. for a short period, e.g., 24-72 hours. Apart from the therapeutic benefits of hypothermia, the outcomes for brain trauma or ischemia patients that develop fevers is worse than for patients that do not develop fevers. Consequently, temperature management for such patients is important, even when hypothermia is not to be used to treat the patients.
The affected organ, in any case, is the brain. Accordingly, systems and methods have been disclosed that propose cooling blood flowing to the brain through the carotid artery. An example of such systems and methods is disclosed in co-pending U.S. patent application Ser. No. 09/063,984, filed Apr. 21, 1998, owned by the present assignee and incorporated herein by reference. In the referenced application, various catheters are disclosed which can be advanced into a patient's carotid artery and through which coolant can be pumped in a closed circuit, to remove heat from the blood in the carotid artery and thereby cool the brain. The referenced devices have the advantage over other methods of cooling (e.g., wrapping patients in cold blankets) of being controllable, relatively easy to use, and of being capable of rapidly cooling and maintaining blood temperature at a desired set point.
As recognized in co-pending U.S. patent application Ser. No. 09/133,813, filed Aug. 13, 1998, owned by the present assignee and incorporated herein by reference, the above-mentioned advantages in treating brain trauma/ischemic patients by cooling can also be realized by cooling the patient's entire body, i.e., by inducing systemic hypothermia. The advantage of systemic hypothermia is that, as recognized by the present assignee, to induce systemic hypothermia a cooling catheter or other cooling device need not be advanced into the blood supply of the brain, but rather can be easily and quickly placed into the relatively large vena cava of the central venous system.
Moreover, since many patients already are intubated with central venous catheters for other clinically approved purposes anyway, providing a central venous catheter that can also cool the blood, if only to manage temperature and thereby ameliorate fever spikes, requires no additional surgical procedures for those patients. A cooling central venous catheter is disclosed in the present assignee's co-pending U.S. patent application Ser. No. 09/253,109, filed Feb. 19, 1999 and incorporated herein by reference.
To supply coolant such as saline to the above-disclosed catheters, a cooling system such as the present assignee's system disclosed in co-pending U.S. patent application Ser. No. 09/220,897, filed Dec. 24, 1998 and incorporated herein by reference, can be used to remove heat from the coolant and return the coolant to the catheter in a closed loop heat exchange system. An alternate system is the thermoelectric cooler (TEC)-based system owned by the present assignee and disclosed in co-pending U.S. patent application Ser. No. 09/260,950, filed Mar. 2, 1999, also incorporated herein by reference. In any case, a cooling system controller preferably maintains temperature at a desired setpoint, be it normothermic or hypothermic. As recognized herein, to facilitate such temperature maintenance, it is necessary to measure patient temperature.
As understood by the present invention, esophageal temperature is a preferred parameter to use because it is more sensitive to body core temperature changes than, e.g., rectal temperature. As also understood by the present invention, for ease of use and to avoid burdensome sterilization procedures, the portion of an esophageal temperature sensor that is advanced into a patient should be disposable. Portions not in contact with the patient, however, need not be disposable. The present invention is provided with these considerations in mind.